(a) Technical Field
The present invention relates to a composite for a temperature sensor, and a method of manufacturing the same.
(b) Background Art
As the number of vehicles being used around the world has increased, the consumption of fossil fuels such as gasoline, diesel, kerosene, liquid natural gas (LNG), and liquid propane gas (LPG) has also increased. At the same time the limited supply of these fossil fuels has been gradually depleted, the price of oil has sharply risen. Thus, there is a need to improve the fuel efficiency of vehicles.
Also, as a result of the accumulation of greenhouse gases, the environmental standards applied to the regulation of exhaust gas have been tightened; consequently, various apparatuses for reducing vehicle emissions that arise during the combustion of a fossil fuel are required.
In particular, the environmental regulations that control the release of dust, NOx, etc., that result from the combustion of diesel fuel have been highly tightened. Thus, there is a need for a post-exhaust apparatus for the re-combustion of such environmental pollutants/gas, or the conversion of such gas into a non-harmful/non-polluting gas.
This type of post-exhaust apparatus shows optimum efficiency when operated at the proper temperature. Consequently, such an apparatus requires a high precision/high durability temperature sensor.
In other words, the temperature sensor of such a post-exhaust apparatus for vehicles can be used at a high temperature of, for example, 500° C. or more. Furthermore, such a temperature sensor must be able to withstand frequent, extreme variations in temperature that may range from room temperature or below, to an operating temperature of 500° C. or above. Additionally, such a temperature sensor must be able to withstand the high vibration that results from the normal operation of a vehicle.
Temperature sensors are typically made of a metal or a metal oxide. If the temperature sensor is to be used at a high temperature, then a metal oxide temperature sensor is generally used. To manufacture a metal oxide temperature sensor according to the conventional art, a test piece of a transition metal oxide such as Fe2O3—NiO—Cr2O3—MnO2 is initially manufactured by a ceramic process of mixing, calcining, and sintering. After the test piece is manufactured, an electrode is printed or plated on the test piece surface. Then, an electrode wire (lead wire) made of Ni, Pt, Au, Cu, or the like, is bonded on the electrode so as to manufacture the temperature sensor. Disadvantageously, the use of transition metals alone to manufacture such a metal oxide temperature sensor, results in a sensor that cannot accurately measure a resistance at temperatures of 500° C. or more because the resistance is very low (e.g., about several ohms (Ω)). Thus, there is a significant problem with this type of temperature sensor in high temperature applications because the measurement error is large.
Additionally, since the manufacturing process involves printing the test piece surface with an electrode made of Ag, Au, Pt, or the like, which is then attached with an electrode wire or pin, the electrode wire or pin is a connection point that is sensitive to temperature and vibration. For example, the electrode may become detached from the device surface under conditions of high temperature and/or high vibration, as is typically found during the operation of a vehicle. Accordingly, another disadvantage of this type of sensor is that it is prone to failure with normal vehicle use, and subject to frequent replacement. Accordingly, there is a need for a temperature sensor that provides accurate readings at high operating temperatures, and is durable under the high temperature and high vibration conditions that are normally associated with operation of a vehicle.